Oasis warm light, same setting different tones?

[Deskisamess]

We've owned 2 of the same model front Kindle a few times. The light color is always somewhat different when you compare the two. They have never been exactly the same.

This isn't because of ambient light differences, it's because the shades of the actual lights are not exactly the same. It's not because of a camera flash either, it is because they differ from device to device, across the same model line.

[Quoth]

Originally Posted by DuckieTigger

Occam's razor only leaves one answer as the most likely: the picture is legit, the devices have a different white balance without the warm leds turned on.

White LEDs don't exist. They are blue, violet or near UV LEDs with at least a yellow phosphor.
So indeed different batches might have a different shade due to phosphor used by LED maker, or different source of LEDs.
Warmth may be simulated by having native pure orange LEDs among the so called "white" LEDs as this is much cheaper than RGB LEDs (used on a few backlighted LCDs and some eink front lights)

There are triple chip LEDs, that have red, green and blue leds and a diffuser. These make a more fake white, like CRT, big LED hall displays and plasma. The OLED displays don't use real LEDs, but electroluminescent diode amorphous printed "dots" often with phosphors to get the exact red, green and blue. Some use also yellow pixels. Some might use native colours. Some use a colour filter overlay like all full colour LCDs do
see https://en.wikipedia.org/wiki/AMOLED and https://en.wikipedia.org/wiki/OLED

[DuckieTigger]

Originally Posted by Quoth

White LEDs don't exist. They are blue, violet or near UV LEDs with at least a yellow phosphor.
So indeed different batches might have a different shade due to phosphor used by LED maker, or different source of LEDs.
Warmth may be simulated by having native pure orange LEDs among the so called "white" LEDs as this is much cheaper than RGB LEDs (used on a few backlighted LCDs and some eink front lights)

The white leds you are saying don't exist, because you want to call them blue with yellow phosphor, indeed have production variations even within the same production run. That is what sorting and matching is for if customer requirements are tight enough.

I would be interested to know which company and model uses rgb leds for their front lit eink devices. Unless you merely say it is possible, in theory.

[Quoth]

Originally Posted by DuckieTigger

I would be interested to know which company and model uses rgb leds for their front lit eink devices. Unless you merely say it is possible, in theory.

I thought I read about a model (1) mentioned on this site that didn't just dim the white LEDs and brighten orange ones, but had adjustable colour? But maybe the comment was about colour temperature.
Certainly the only reasons not to have real RGB LEDs are:

• Cost of the LEDs.
• Maybe controller cost is slightly more.
• Space and losses of the diffuser. Cheap ones without a diffuser change colour with view angle as it's three chips. Perhaps not a problem with clever combined lightpipe diffuser design.
• Extra wiring and controller complexity.

My background is in Electronics design and programming, even two CE handheld devices. So I know what real colours of LEDs there are (basic doping / materials) which all are monochromatic. White appearance LEDs are using a phosphor or a mix of phosphors on blue, violet or near UV, just like CFL, CCFL etc.

The thickness of the phosphor affects the colour and the brightness. Decent quality ones from the same batch look the same. The colour of any actual real LED does shift a little with temperature and current drive, not significant. It doesn't change with production has that's set by the physics, the bandgap voltage, which is why single chip IR LEDs have the lowest voltage and near UV LEDs the highest voltage. Green typically have a voltage nearly halfway between red and blue types, about 2.2V. High Intensity red are a different physics to older red and thus a higher voltage.

[murraypaul]

Originally Posted by DuckieTigger

I would be interested to know which company and model uses rgb leds for their front lit eink devices. Unless you merely say it is possible, in theory.

The Kobo Aura One has a combination of white LEDs for brightness and RGB LEDs for colour changing.

[stumped]

i am guessing the the blue light filters on LCD tablets use a different method, to suck some of the blue out of the colour display
I found a setting on my Huwaei tabet which turns on a filter at a set time of evening. that works for me because I am done streaming video by than and will only be using tablet for reading
with Kobo, I have that set to auto filter based on time of day - that also works well

[DuckieTigger]

Originally Posted by murraypaul

The Kobo Aura One has a combination of white LEDs for brightness and RGB LEDs for colour changing.

Interesting. I have not heard any (developmental) settings to user change the color of the rgb leds that is added to the white ones. But then the controller may not be capable of adjusting the red, green, and blue individually.

Could explain why some Kobos and Tolinos are defective by turning green instead of orange when warm setting is all the way up.

[j.p.s]

Originally Posted by stumped

i am guessing the the blue light filters on LCD tablets use a different method, to suck some of the blue out of the colour display
I found a setting on my Huwaei tabet which turns on a filter at a set time of evening. that works for me because I am done streaming video by than and will only be using tablet for reading
with Kobo, I have that set to auto filter based on time of day - that also works well

LCDs are illuminated from behind by a "white" light. An LCD color pixel usually consists of 3 sub-pixels, each topped by a red, green, or blue filter. A particular color for a pixel is determined by controlling the amount of light transmitted by the liquid crystal cell of each sub-pixel.

The "blue light filter" is software that applies an additional dimming factor to all blue sub-pixels. There is no need to speculate about this stuff. The information is widely available.

[Quoth]

Indeed the exact same LCD software will work on a TV, phone, laptop, tablet, monitor if implemented. Independent of the HW used for the backlight. The earlier Nokia N9210 communicator used CCFL tubes and the N9210i used some sort of LED backlighting.
One of my HDTVs is CCFL tubes and a later model (with inferior selection of inputs) has LED backlights. Cheaper TVs/Monitors/Laptop only use LEDs on the edges. Some netbooks used too few and only on the top edge, so you see a row of cone shaped furrows if the screen is mostly white. Makes poorly Forma front lights look good!

Only some very very expensive TVs have arrays of R G B LED backlights for the LCD to increase contrast and saturation on large areas. It's an unnatural effect best turned off!

*Regular fluorescent tubes and folded / curled CFL have a heating coil at each end momentarily powered till the tube is warm to aid electron emission. Sodium lighting has neon to get the sodium vaporised while the tube warms, hence orange to pink glow when started. CCFL are Cold Cathode discharge tubes and use a much higher voltage:
https://en.wikipedia.org/wiki/Fluore...orescent_lamps
The cost, fragility and need for a high voltage supply means CCFL were replaced by LEDs. They do last well, I've one laptop 20 years old still good. The colour rendition is easier to be good than LEDs. Cheap "White" LEDs are a bit purple and get worse as the phosphor ages. Better ones use more expensive phosphors and near UV LEDs.

[jackie_w]

Originally Posted by DuckieTigger

Interesting. I have not heard any (developmental) settings to user change the color of the rgb leds that is added to the white ones. But then the controller may not be capable of adjusting the red, green, and blue individually.

If you switch on the Developer Options on a Kobo AuraOne there is a screen available with 4 sliders where you can set each of Red, Green, Blue, White independently anywhere between 0-100%. You can have any temporary screen colour you fancy, green, hot pink, electric blue, purple ... if you really want it

Despite this the AuraOne has many reports (including mine) of uneven colour when the standard colour temperature feature is set to max-orange. Maybe those RGB LEDs weren't such a good idea after all. It seems to be the Green component which causes the unevenness on mine.

[Quoth]

I'd not design R G B leds into anything without very well tested diffusers. They are three separate chips in one package, so it's very tricky to mount the packages, diffuser, light pipe etc and have it even.

[Richwood]

Does the Oasis actually use full spectrum adjustable output RGB LEDs or 1/2 cool white and 1/2 warm white to yellow output LEDs and vary the output of each type depending on the color temperature setting adjustment? I find the latter more likely as otherwise why 25 LEDs being used on the Oasis G10 and 12 for the G9. The warm LEDs are phosphor coated to give the warmer light I believe and there is going to be factory variations in the coating thickness which will affect the color temperature output. The human eye is amazingly color sensitive which is why things like pearl color matching in Japan is so labor intensive. Not too surprising to me that there is some variation unit to unit in color of the warm lighting on the Oasis readers. IMO probably unavoidable with manufacturing tolerances on electronic components.

[Quoth]

NO RGB LED is full spectrum. They have narrow peaks in Red, Green and Blue to match the peaks in our RGB colour perception, so colours can be simulated as they are on TV or monitor or phone screen. Colour displays are trick.

If you illuminate real world objects purely by R G B LEDs some colours are wrong and some are dark. White CFL, CCFL and "White" LEDs use a mix of phosphors. Unlike real LED chips without phosphor, a phosphor has a broader spectrum. A mix can provide good colour rendition for illumination of a room. This can be unconnected to Colour Temperature! You can get any Colour Temperature from R, G & B LED light combined.
https://en.wikipedia.org/wiki/Color_rendering_index

ALL "white" LEDs are really blue, violet or near UV. The R G B LEDs never have a phosphor as that would reduce the output. The blue LED chip in an R G B package is chosen to be closer to the eye's blue peak. A blue LED chip for a white LED uses a mainly yellow phosphor mix (other colours included) will ideally be shorter wavelength to be more efficient producing the Red to Green part of the spectrum via the yellow phosphor. Very cheap white LED lighting can lack the Cyan part of the spectrum, so illuminated cyan objects will look greener, bluer or darker or even grey!

We are far more sensitive to hue than brightness or saturation.

[DuckieTigger]

Originally Posted by Richwood

Does the Oasis actually use full spectrum adjustable output RGB LEDs or 1/2 cool white and 1/2 warm white to yellow output LEDs and vary the output of each type depending on the color temperature setting adjustment? I find the latter more likely as otherwise why 25 LEDs being used on the Oasis G10 and 12 for the G9. The warm LEDs are phosphor coated to give the warmer light I believe and there is going to be factory variations in the coating thickness which will affect the color temperature output. The human eye is amazingly color sensitive which is why things like pearl color matching in Japan is so labor intensive. Not too surprising to me that there is some variation unit to unit in color of the warm lighting on the Oasis readers. IMO probably unavoidable with manufacturing tolerances on electronic components.

It appears that there is white leds without warm setting, and additionally yellow/orange added on top when warm setting is enabled. My Oasis 2 and the Oasis 3 look near identical without warm.

Attached are some pictures showing how warm setting changes at 0,8,16, and 24 setting. The Oasis 2 on the left as reference unchanged. To my eyes it looks more yellow in real life, but I chose manual white balance setting of 6600°. Not sure how to set my phone screen to 6600°, so that the picture matches. Otherwise with automatic white balance the Oasis 2 changes color as well.